1. Field of the Invention
The present invention relates to a disc drive unit and a disc unit and more particularly a disc drive unit for rotating an optical disc, a magnetic disc or the like which is used as a recording medium in the data processing systems and a disc unit equipped with said disc drive unit and a read-write head for reading and writing data out of and onto the surface of a disc.
2. Description of the Prior Art
A conventional disc drive unit with the construction shown in FIG. 1 has been well known to those skilled in the art. A shaft 1 is supported by a pair of vertically spaced-apart bearings 2a and 2b which in turn are securely mounted on a base 3. A turntable 4 made of a nonmagnetic material is securely attached to the upper portion of the shaft 1 in coaxial relationship therewith. An annular recess 4a is defined at the upper surface of the turntable 4 coaxially thereof and a disc attraction magnet 6 is fitted through a yoke 5 into the recess 4a. Plate-like yokes 8 are securely attached to the undersurface of the turntable 4 with screws 7, and driving magnets 9, which constitute a disc driving motor, are securely attached to the undersurfaces of the yokes 8. Yokes 10 which establish magnetic circuits together with the yokes 8 are securely mounted on the base 3 in opposing relationship with the yokes 8, respectively. A driving coil 11, which is also a component part of the disc driving motor, is mounted on each yoke 10.
In the case of the disc drive unit with the above-described construction, a disc is mounted on the turntable 4 while the position of the center of the disc is determined by the shaft 1. When a suitable current is supplied to the coils 11, the magnetic circuits made of the coils 11 produces a rotating force so that the turntable 4 is caused to rotate about the shaft 1 relative to the base 3.
FIG. 2 illustrates the construction of another conventional disc drive unit incorporated in an optomagnetic type disc unit. The center portion of an optical disc 100, which is used as a recording medium, is increased in thickness as compared with the remaining portion to define a hub 100a, and a center hole 100b is defined at the center thereof. A magnetic plate 101 such as a plate of iron or the like is securely attached to the undersurface of the hub 100a.
The optical disc 100 which is mounted on the turntable 4 is rotated by a motor 60 through the turntable 4. The turntable 4 upon which the optical disc 100 is mounted is securely attached to the upper portion of the shaft 1 which in turn is rotated by the motor 60. A disc-shaped recess is formed at the upper surface of the turntable 4 and the plate-shaped disc attraction magnets 6 are mounted through the yokes 5 at the bottom of the disc-shaped recess.
The optical disc 100 is mounted on the turntable 4 by a loading mechanism (not shown) and is supported by the turntable 4. More particularly, the position of the optical disc 100 is determined when the shaft 1 is inserted into the center hole 100b, and the optical disc 100 is placed on a flange 4b which is defined by extending the peripheral portion of the turntable 4 radially, upwardly and obliquely, while the magnetic plate 101 is attracted by the magnet 6 so that the disc 100 is supported by the flange 4b.
Thus the optical disc 100 is rotated by the motor 60 while it is mounted on the turntable 4 in the manner described above. Then a read-write head 50 is displaced in the radial direction of the optical disc 100 so that data is written onto or read out off of the surface of the optical disc 100 by the optomagnetic recording system.
In response to the tendency for miniaturization and for facilitating the portability of data processing units such as microcomputers, wordprocessors and the like each incorporating a disc drive unit, there exists a strong demand for miniaturizing and especially decreasing the thickness in the direction perpendicular to the disc mounted an the disc drive units and the disc units equipped with the disc drive unit. Such miniaturization and reduction in thickness can be sometimes accomplished by a simple design of the component parts and a reduction in the number of such parts. The successful reduction in size of the disc driving units and disc units can attain the advantages that the costs can be decreased due to an increase in production efficiency. Also, a high degree of reliability in operation can be ensured.
Even in the conventional disc drive units and disc units, various countermeasures for the reduction in thickness have been devised and demonstrated. For instance, in the case of the disc drive unit as shown in FIG. 1, it is so designed and constructed that the turntable upon which the disc is mounted and which is rotated functions as part of the rotor of the disc driving motor, whereby the number of component parts to be assembled into the disc drive unit is decreased. It is furthermore proposed to shorten the distance between the vertically spaced-apart bearings used in the disc drive units shown in FIGS. 1 and 2 as much as possible while leaving a suitable air gap between the driving magnet and the coil mounted thereon. Moreover, it is proposed to construct the magnets 6, yokes 5 and turntable 4 into a unitary body; that is, to magnetize the turntable 4 in the constructions shown in FIGS. 1 and 2.
However, even when the turntable is so designed and constructed that it accomplishes the double function of the turntable and the rotor as described above, there still remains the possibility of decreasing the thickness of the disc driving unit. When the distance between the vertically spaced-apart bearings is shortened, oscillation of the shaft results so that the disc cannot rotate at a predetermined rotational speed. Furthermore, in the case of the magnetization of the turntable, there is a fear that magnetic particles separated from the disc may adhere to the flange of the turntable on which the disc is placed by the magnetic attraction force of the turntable. As a result, waving of the disc mounted on the flange results so that the correct read/write operation is adversely affected.
As described above, in the many conventional disc drive units and disc units, there still remains the possibility for reducing the thickness. Furthermore, even when suitable countermeasures are used so as to decrease the thickness of the disc drive units and disc units, adverse effects result due to the use of such countermeasures.